Abstracts

Rationale: Language deficits are common in epilepsy and have led to increased investigation in associated white matter tracts. The aim of this series is to evaluate white matter (WM) integrity before and after surgical resection of a seizure focus targeting the arcuate fasiculus (AF), a major WM pathway connecting frontal and parietal association areas important for language reception and production. We investigate how the structural connectivity between AF pathways ipsilateral and contralateral to the seizure focus measured by fractional anisotropy (FA) changes following focal topectomy in pediatric patients with intractable epilepsy. Methods: Using a 3T scanner, MRI data were acquired on 3 pediatric patients with intractable seizures before surgery and 6-12 months after surgery. DTI data was processed and analyzed using FSL v4.1.7. FSL was used to conduct probabilistic tractography of the AF in each hemisphere. FA values were recorded for each AF which correlates with structural connectivity. Pathology was also performed on resected specimens. Results: In all patients, AF pathways in each hemisphere crossed through the splenium of the corpus callosum before surgery. Following surgery, the spatial extent and strength of structural connectivity and FA values between AF pathways changed. In two patients where focal cortical dysplasia was found to underlie the epileptic focus, FA values were increased in both hemispheres. In the other patient, the epileptic focus pathology was consistent with heterotopic neurons and FA values increased in the contralateral hemisphere but were reduced in ipsilateral hemisphere following resective surgery. Conclusions: Patients with focal cortical dysplasia tend to have better prognosis and less related neurologic compromise than patients with heterotopic neurons which may be more widely distributed. Finding increased FA values in the contralateral hemispheres after resection were consistent with previous reports suggesting an influence from the ipsilateral focus. Increases in ipsilateral FA value in resected focal dysplasia suggest removal of factors prohibiting typical connectivity. The lack of an ipsilateral increase in the patient with heterotopia may indicate persistence of anomalies (apart from the seizure focus) that affect normal neurologic function.